Process for extracting saponins from plant tissue



United States Patento 2,791,581 PROCESS FOR EXTRACTING SAPONINS FROMPLANT TISSUE Monroe E. Wall, Oreland, and Edward S. Rothman,Philadelphia, Pa., assignors to the United States of America asrepresented by the Secretary of Agriculture No Drawing. Application May1, 1956, Serial No. 582,052 9 Claims. (Cl. 260-2105) (Granted underTitle 35, U. S. Code (1952), sec. 266) A non-exclusive, irrevocable,royalty-free license in the invention herein described, for allgovernmental purposes, throughout the world, with power to grantsublic'enses for such purposes, is hereby granted to the Government ofthe United States of America.

This application is a continuation-in-part of our copending applicationof the same title, filed December 2, 1952, Serial No. 323,736, nowabandoned.

This invention relates to steroidal saponins and to processes for theirisolation from plant tissue containing them.

An object of this invention is to provide efficient and economicalprocesses for extracting steroidal saponins from the plant tissues inwhich they are found in nature. Another object is to provide a processfor the extraction of such saponins from plant tissue which avoids theuse of benzene or other volatile, inflammable and poisonous hydrocarbonsolvent.

Steroidal saponins are glucosides of steroidal sapogenins and occur inmany plant species. The sapogenins obtainable from them by hydrolysisare useful in medical and pharmaceutical applications.

Conventional processes for recovering saponins from the plant tissues inwhich they are produced by nature include tedious and expensiveextraction steps in which large volumes of benzene and similar hazardoushydrocarbon solvents are used.

Our present invention is an improvement on the process described in ourcopending application entitled Process for Preparation of Saponins,filed September 5, 1952, Serial No. 308,174, U. S. Patent 2,715,122.

We have discovered that steroidal saponins can be economically extractedfrom steroidal saponin-containing fresh or dried plant tissue,particularly such tissue which is derived from the plants Agave andYucca, and recovered in sufficient purity for most purposes byextracting the plant tissue with a hot water-miscible saponin solventcontaining at least 5% water, with the remainder, if any, being awater-miscible alkanol, as for example, ethanol and isopropanol. Theresulting solution is converted to an essentially aqueous solution byconcentrating it, as by removing most of the alkanol, if present, to apoint short of causing appreciable separation of the steroidal saponinsand separating, as by filtration, any precipitated solids, as forexample, insoluble fatty materials. The steroidal saponins are thenextracted from the essentially aqueous solution with a water-immisciblealcohol of from 4 to 6 carbon atoms, preferably butanol, as a solventfor the steroidal saponins. Thereafter, the steroidal saponins areisolated from the resulting alcoholic solution, as for ex ample, byadding water to the alcoholic solution, and distilling off the solvent,thus converting again to an essentially aqueous solution of partiallypurified saponins. When the saponins are to be recovered as such, thisisolation procedure of adding water to the alcoholic solution toreconvert to the essentially aqueous solution may be omitted and thesaponins recovered directly by distillation of the water-immisciblesolvent, preferably in vacuo.

Usually, the saponins are to be used immediately for recovery ofsapogenins, in which case the aqueous solution produced in the isolationprocedure described above, that is, by adding water to the alcoholicsolution and 2 distilling off the solvent, is acidified and heated tohydrolyze the saponins; the resulting crude sapogenins are recovered andpurified, suitably by the process of Wall described in his copendingapplication entitled Isolation of .Sapogenins, filed December 2, 1952,Serial No. 323,735.

In extracting the plant tissue with the Water-miscible saponin solvent,above, we prefer to use an aqueous solution of a water-miscible alkanol,though we can use pure water. The preferred alcoholic solution is 50-80%alkanol for use with dry plant material and -95% with fresh plantmaterial.

In extracting thesteroidal saponins from the essentially aqueoussolution with the water-immiscible alcohol we prefer to use butanol butcan also use any water-immiscible alcohol of 4 to 6 carbon atoms, as forinstance, isobutanol, see-butanol, amyl alcohol, hexanol,2-ethylbutanol, methylamyl alcohol or cyclohexanol.

EXAMPLE I Five kilograms of dry yucca leaf meal was extracted with 25 l.of boiling 80% isopropanol20% water. The solution was cooled, filteredand concentrated to 4 l. The essentially aqueous concentrate wasfiltered hot to remove precipitated fatty materials and other impuritiesand the precipitate was washed with hot 50% isopropan0l50% Water. Thecombined filtrates were again concentrated to 4 1. and were extracted 4times with butanol, 1 1. being used each time. Two liters of water wereadded to the combined butanol extracts and the butanol-water azeotropewas distilled to remove the hutanol. The aqueous residual solution wasfurther concentrated to 1 l.

The partially purified saponin in the aqueous solution was thenhydrolyzed to sapogenin and the resulting sapogenin recovered andpurified as described in the copending application of Wall mentionedabove. There was thus obtained 50 g. of substantially puresarsasapogenin.

EXAMPLE II Forty pounds of fresh Agave toumeyamz leaves were extractedwith 40 l. of boiling ethanol. The extract was then processed asdescribed in Example I.

The partially purified saponins in the final aqueous solution werehydrolyzed as in the previous example and the final yield was 36 g. of a50:50 mixture of substantially pure hecogenin and manogenin.

By proceeding substantially as described in the above examples, numeroussteroidal saponins were isolated from a great variety of plant material.Table I, following, summarizes the plant sources and the saponinsisolated in a typical group of these experiments.

Table l.Sap0nins isolated from plant sources Species Part SaponinDioscorea spiculiflora gentronin.

Do correllonin. .Dzoscorea bartlettiiyamoniu. Dioscorea composite.dioscin. Dioscorea macrostach kryptonin. Agave lechcguz'lla smilonin.Agave magoensis yucconin. Agave toumeyana.-. heconin.

Do d manonin.

D0 gitonin.

m a d Q-dchydrohcconin.

Agave uelso'nii do Q-dehydromanonin. Chlorogalum pomcridiauum tuberchloronin. Yucca l is... leaf tigonin. Yucca schidz'gem do sarsasaponin.

Do .1 do markonin. Yucca filammtosa do kammonin. Yucca gloriosa doheconin. Yucca whipplei do tigonin. Yucca camerosana fiower samonin..Manfreda sp tuber gitonin. Digitalis purpurea 1eaf digltonin.

We claim:

1. A process comprising extracting the steroidal saponins from steroidalsaponin-containing plant tissue with a hot water-miscible saponinsolvent containing at least 5% water with the remainder, it any, being awaterrniscible alkanol, converting the resulting solution to .anessentially aqueous solution by concentrating it 'sufliciently to removemost of the alkanol, if present, to a point short of causing appreciableseparation of the steroidal saponins and separating any precipitatedsolids, extracting the steroidal saponins from the essentially aqueoussolution with a water-immiscible alcohol of from 4 to 6 carbon atoms asa solvent for the said steroidal saponins, and isolating the steroidalsaponins from the resulting alcoholic solution.

2. The process of claim 1 wherein the water-miscible alkanol is ethanol.

3. The process of claim 1 wherein the water-miscible alkanol isisopropanol.

'4. The process of claim 1 wherein the water-immiscible alcohol isbutanol.

5. The process of claim 1 wherein the Water-miscible alkanol is ethanoland the water-immiscible alcohol is butanol. V p

6. The process of claim 1 wherein the water-miscible alkanol isisopropanol and the water-immiscible alcohol is butanol.

7. The process of claim 1 wherein the plant tissue is derived fromAgave.

8. The process of claim 1 wherein the plant tissue is derived from Agavetoumeyana.

9. The process of claim 1 wherein the plant tissue is derived fromYucca.

References Cited in the file of this patent UNITED STATES PATENTS2,715,122 Rothman et al Aug. 9, 1955

1. A PROCESS COMPRISING EXTRACATING THE STEROIDAL SAPONINS FROMSTEROIDAL SAPONIN-CONTAINING PLANT TISSUE WITH A HOT WATER-MISCIBLESAPONIN SOLVENT CONTAINING AT LEAST 5% WATER WITH THE REMAINDER, IF ANY,BEING A WATERMISCIBLE ALKANOL, CONVERTING THE RESULTING SOLUTION TO ANESSENTIALLY AQUEOUS SOLUTION BY CONCENTRATING IT SUFFICIENTLY TO REMOVEMOST OF THE ALKANOL, IF PRESENT, TO A POINT SHORT OF CAUSING APPRECIABLESEPARATION SOLIDS, STERIDAL SAPONINS AND SEPARATING ANY PRECIPITATEDSOLIDS, EXTRACTING THE STEROIDAL SAPONINS FROM THE ESSENTIALLY AQUEOUSSOLUTION WITH A WATER-IMMISCIBLE ALCOHOL OF FROM 4 TO 6 CARBON ATOMS ASA SOLVENT FOR THE SAID STEROIDAL SAPONINS, AND ISOLATING THE STEROIDALSAPONINS FROM THE RESULTING ALCOHOLIC SOLUTION.